Abstract: The high cooling rate during laser welding process may prompt the occurrence of solidification cracking,which is directly related to the existence of residual liquid metal in the solidification temperature range.In this paper,the in-situ observation of residual liquid metal at the trailing edge of the weld pool with optical microscope was conducted directly with high speed and high magnification during laser welding of SUS304,SUS316 and SUS310S austenite stainless steels.The solidification behavior under different welding speeds was analyzed.It was found that the in-situ observed residual liquid metal was a part of the coexistence zone of liquid and solid during solidification process.The order of in-situ observed existence range of residual liquid metal was in good correspondence with the solidification cracking susceptibility,which was obtained by fan-shaped hot cracking test.